Arc'teryx Rho Heavyweight Base Layer Bottom Men'sThe Rho Heavyweight Arc'teryx's warmest base layer pant is made for cold days and mixed output. On the move, the Polartec Power Stretch Pro stretches for outstanding freedom of movement. During rest phases or when it gets really cold the men's Rho Heavyweight Bottom's soft brushed interior traps heat to keep you warm. The fleece's durable nylon outer has a smooth face for comfort under layers, and a zippered thigh pocket secures small essentials.